Hints on Flying the Pilatus B4 This is an English summary of Jochen Reuter's paper, published on the SAGA-website www.sagach.ch I could not resist adding a few hints of my own, where I saw it appropriate. But overall, it is still Jochen's text. And I was too lazy to convert any units of measurement from metric to English. If you prefer to go by knots and pounds etc. you will have to juggle the units yourself. General Remarks Any pilot, who is new to the B4 will notice that it is a "noisy" glider. The "blonk-blonk" of the skin panels can upset a novice, but after a few flights you get used to it and before long you'll ignore it. Jochen's B4 came from the UK and a previous owner had apparently tried to turn it into a high-performance machine. All the skin joints and rivet heads had been covered and smoothed. But if you intend to do aerobatics, this is not a good idea at all. Apart from the additional weight and lots of useless work, the putty becomes brittle with time and when the structure is flexing, will crack and eventually peel off. Talking about C of G: Jochen is very tall and weighs around 100 kg. So he flies at the load limit and also the forward CG limit. Earlier, he used to fly with the small tail ballast weight (2.3 kg), mainly to facilitate spinning, but now he recommends even for heavy pilots not to. In his opinion, the B4 handles better with a forward CG. I am somewhat lighter, ca. 80 kg with parachute, and SAGA's B4 which has an authorised load range of 55 to 104 kg handles ideally at my weight. The trim should be set nose-down for aerobatics.Hands-off speed should be around 150 km/h. This way you do not need so much down elevator in most manoeuvres. It may be a good idea, before you start with aerobatics, to check and adjust the control deflections. Find someone who is capable and authorised to do it. Particularly the ailerons should be adjusted to the very limits. You can use every single degree of aileron deflection for better rollrate. If you want to do aerobatics seriously, aiming-sticks on the wingtips are a MUST. Without, you are unable to judge your attitude accurately. The sticks should be aligned parallel to the longitudinal axis, not to the zero-lift axis. If you fly the B4 with the zero-lift axis vertical, the nose points nearly 10° forward on the way up and back on the way down. In principle, aerobatic judges must take this into account, but in practise THEY DON'T! Also put strings on your aiming sticks. In a tailslide, they are the best indicators when to pull back or push forward. If you want to try flicks, please be gentle! The version PC11 AF has a strengthened rear fuselage and is certified to do flicks. Nevertheless, keep in mind that all our B4s are at least 36 years old (as long as they were not produced in Japan). The structure does not get any stronger with time and the torsional loads on the rear fuselage are considerable in flicks. Entry Speeds and Operating Limits In general, you can fly practically all the manoeuvres with the speeds you are used to from the ASK 21. But in a normal Advanced sequence, you will not have any height problems with the B4, so Jochen recommends to fly a bit faster. 190 km/h should do. The main weaknesses of the B4 are its low VNE of 240 km/h and VA of 163 km/h. This becomes most critical in vertical down-lines. It is impossible to stabilise the down-line for any length of time without coming out at or near the redline. Be extra careful never to go into a vertical down-line from too high an airspeed. The low VA in my opinion is not so much of a problem. As long as you remember to be easy on the elevator in pullouts from high speed, you are not likely to overstress the airframe. True, torsional loads on the wings from aileron deflection increase by the square of the speed. On the other hand, you can't avoid exceeding the VA with full aileron deflection, if you want to fly figures, which are required in today's Advanced competitions. But under any circumstances avoid to apply large aileron inputs while pulling g at the same time. The resulting torsional loads add to the bending loads and may well overstress the wings. Individual Figures All entry speeds are 190 km/h, unless stated otherwise. Loops Pullup no more than 4 g. Over the top release back pressure not before the nose touches the horizon. Then let it go "ballistic" till the nose points down 30-40°. Seat pressure should remain positive at a fraction of one g over the top. On the way down, avoid pulling too early or too hard. Otherwise, you end up with a "9" instead of a nice, round loop. Aileron Rolls Main problem is the B4's relatively sluggish roll rate; but if you are used to the ASK 21, it may still appear quick to you. Never roll with lots of top rudder! Particularly in the second knife-edge, if you apply too much top rudder, the airflow over the vertical tail may stall and the B4 falls out of the figure doing a funny kind of wobble. It's not dangerous, but it looks awful. We found that rolls look best with neutral rudder all the way. It is not necessary to lift the nose over the horizon for the start of the roll, but beginning in the first knife-edge, the direction must be maintained with down elevator and the nose must be pushed a few degrees above the horizon in the inverted position. Maintain the down elevator into the second knife-edge. Otherwise, you will turn away from the direction of roll in the final 2 quarter. The correct dosage of elevator control is the secret to good-looking rolls in the B4 and can only be learned with lots of practise. Two-Point-Rolls Fly it like the full aileron roll; just stop it in the inverted. Don't forget to push the nose above the horizon in the inverted stop. The greatest difficulty is again the correct application of down elevator, to avoid a "corkscrew" in the second half of the roll. Practise, practise, practise… Four-Point Rolls Due to the slow rollrate, the stops must be long enough to be clearly recognisable. Contrary to the full aileron roll, the nose should be raised a little before the start of the four- point, but don't overdo it. Do not use top rudder in the knife-edge stops! Correct for the nose-drop by deliberately raising the nose in the inverted stop. When you plan your Free sequence, don't do a full four-point! It'll take forever and you'll need the entire length of the box. Superslow Roll Quite difficult! Practise counting the seconds, this helps keeping the rollrate constant. I use much the same technique as for a roll with the ASK 21 (which takes at least 12 sec.). Start with the nose above the horizon. Keep the nose up with elevator till you approach the knife-edge. In the first knife-edge, start pushing the nose "out" and up. In the inverted it must be markedly above the horizon. Maintain down elevator into the second knife-edge to control the direction. In the last quarter (past the second knife-edge), I apply some top rudder (gently!) to keep it from turning away as I come out of the roll. Again, proper elevator control is the secret! Stall Turns Nice to fly; looking very good, but only with the right technique… In German we call it "Vorspannen" = tensioning. I am not quite sure that you are familiar with it. The trick is to establish a slight sideslip on the vertical up-line in the direction you want to turn. Look at the inside wingtip before you start the pullup. Then, you can either dip the inside wing a FEW degrees before pulling or apply some aileron in the direction of turn during the pullup. Going up vertically, you must then use opposite rudder to keep the inside wingtip on the horizon. As speed decreases, opposite rudder deflection is increased up to the point where you apply full rudder in the direction of turn. This drawing of another Pilatus aircraft illustrates it. I took it from the book "Flight Unlimited" by famous Swiss aerobatic pilot Eric Mueller. Due to it's high-lift airfoil, the B4 wants to raise the nose during the turnaround. You must counteract with some down elevator. 3 On the way down it may be necessary to push again in order to stay vertical, but again, don't overdo it. Tailslides Canopy-up tailslides are more tricky in the B4 than canopy-down. The obvious reason is the difference of nearly ten degrees between longitudinal axis and zero-lift axis. From an exactly vertical attitude, the B4 MUST tip over backwards, because the zero-lift axis is inclined about ten degrees back. Therefore, for a canopy-up tailslide, use no more than about 80° nose-up. Jochen writes, his limit is exactly 84°; 85° is already too much. But as a beginner, you'll never be able to control your vertical attitude as exactly… This is how it's done (canopy-up): First, establish a wings-level glide at 200km/h, yaw-string centered.